1. Field of the Invention
The present invention relates to a thermal type-infrared detection device used for non-contact measurement of temperature and prevention of crimes and disasters, a method for manufacturing such the detection device, and an array composed of such the thermal type-infrared detection.
2. Description of the Prior Art
Heretofore, an infrared detection device of thermopile type, pyroelectric type or a bolometer type has been used as the thermal type-infrared detection device as mentioned above, however, an infrared detection section is formed on a diaphragm composed so as to be thermally isolated from a semiconductor substrate for improving the sensitivity in any type of the devices.
Thus, in a case of the thermal type-infrared detection device of thermopile type as an example of the conventional thermal type-infrared detection device, the thermal type infrared detection device 101 has thermal isoplated structure formed through silicon micro-machining technique as shown in FIG. 7.
That is, the thermal type-infrared detection device 101 is provided with a silicon substrate 102 as a semiconductor substrate, a diaphragm 103 made of an insulating material, and an infrared detection section 104 positioned on the diaphragm 103. The silicon substrate 102 is formed with a concave 106 removed by etching the lower part of the diaphragm 103 with silicon etchant infiltrated through an etching aperture 105, accordingly the diaphragm 103 is thermally isolated from the silicon substrate 102 through this concave 106.
The infrared detection section 104 on the diaphragm 103 is provided with a thermopile 110 having a plurality of thermocouples 109 arranged in parallel and electrically connected in series which are composed of n-type semiconductor 107 (e.g. n-type polysilicon) and p-type semiconductor 108 (e.g. p-type polysilicon), and a heat absorption layer 112 stacked on the thermopile 110 through an insulation layer 111. The detection section 104 is so structured as to read an electric signal through lead wires 113 connected with both ends of the thermocouples 109 and made of aluminum or so, and high thermal resisting beam structure is used in order to try to improve the sensitivity of said device 101 in the example shown in the FIG. 7.
In this case, it is possible to apply the method based of surface micro-machining technique using a sacrifice layer, however in any method, the diaphragm 103 has a configuration that the lower part of a cold junction 109C of the thermocouples 109 is formed directly or through a frame-shaped layer on the silicon substrate 102.
Such the infrared detection device 101 forms an array 120 of thermal type-infrared detection device by arranging a plurality of them as shown in FIG. 8. In the thermal type infrared detection device array 120, wires 121 and a device-selection switching mechanism 122 are disposed on the great majority of the substrate area excepting the cold junctions 109C of the thermocouples 109.
However, in the conventional thermal infrared-type detection device as mentioned above, the lower part of the cold junction 109C of the thermocouples 109 is formed directly on the silicon substrate 102, or formed indirectly on the silicon substrate 102 through the frame-shaped layer. Accordingly, the lead wires 113, which are indispensable in the device 101, are distributed in the area of the cold junction 109C of the thermocouple 109 in the case of forming the diaphragm 103 directly on the silicon substrate 102 (the device-selection switching mechanism 122 is disposed in the thermal type infrared detection device array 120), thus, the lead wires 113 and the circuit zone are positioned on the outer peripheral portion of the device, and occupy the greater part of the area assigned for the device.
On the other side, although the wires 113 and the device-selection switching mechanism 122 are disposed at the lower part of the frame-shaped layer in the case of forming the diaphragm 103 on the silicon substrate 102 through the frame-shaped layer, an area out of contact with the cold junction 109C in the area of the frame-shaped layer becomes wider, therefore an area of the heat absorption layer 112, which exert influence directly on the signal of the infrared detection, becomes narrow relatively against the area assigned for the infrared detection device 101. Namely, there is a problem in that an opening rate (hereinafter referred to as xe2x80x9cfill factorxe2x80x9d) of the detection device becomes lower, consequently it may become hard to detect feeble infrared lays, and it is the subject to solve the above-mentioned problem of the conventional infrared detection device.
The present invention is made in view of the above-mentioned problem in the prior art, and it is an object to provide a thermal type-infrared detection device which is possible to enlarge the occupied area of the heat absorption layer by raising the fill factor and possible to improve the sensitivity and the output signal without lowering the strength of the diaphragm, and a production method of the device of this kind, in addition to an array of thermal type-infrared detection device.
The thermal type-infrared detection device according to this invention is characterized by comprising a semiconductor substrate having a concave, a diaphragm made of an insulating material and substantially covering the concave of the semiconductor substrate, and an infrared detecting section positioned on the diaphragm, the semiconductor substrate is provided with a projection made of a thermal conductor for supporting the diaphragm away from the semiconductor substrate. Such the configurations of the thermal type-infrared detection device serve as a means for solving the aforementioned problem of the prior art.
The thermal type-infrared detection device according to respective embodiments of this invention is characterized in that the thermal conductor is made of a silicon-polycrystalline material or a metallic material, or the device is any one of a thermopile type, a bolometer type, and a pyroelectric type.
Moreover, the production method according to this invention is characterized by comprising the steps of preparing a semiconductor substrate formed with a first insulation layer on the surface thereof, removing a part of the first insulation layer of the semiconductor substrate to form an aperture for anisotropic etching of the semiconductor substrate, stacking an etching sacrifice layer on a whole surface including the first insulation layer on the semiconductor substrate and the aperture of the first insulation layer, stacking a diaphragm and a second insulation layer on the etching sacrifice layer in order, infiltrating etchant into the etching sacrifice layer after taking a measure for making the etching sacrifice layer withstand the etchant at a position to be formed with the projection, etching and removing the etching sacrifice layer excepting the position corresponding to the projection, and removing a part of the semiconductor substrate to form the concave through anisotropic etching by infiltrating anisotropic etchant through the aperture of the first insulation layer on the semiconductor substrate at the time of producing the thermal type-infrared detection device according to this invention. Such the configurations of the production method of the infrared detection device serve as a means for solving the aforementioned problem of the prior art.
Furthermore, the array of thermal type-infrared detection device according to this invention is composed of a plurality of the thermal type-infrared detection devices according to this invention arranged with each other, and the array according to an embodiment of this invention is characterized in that projections adjacent to each other of the respective devices are formed in continuous one body.
In the thermal type-infrared detection device according to this invention, the lead wires of the cold junction area are distributed in the lower part of the infrared detection section, the cold junction area of the infrared detection section positioned on the diaphragm and the semiconductor substrate are thermally connected through the projection made of the thermal conductor in a wall or pillar-shape and disposed discontinuously, accordingly an usable area for the heat absorption layer becomes wider without harming mechanical strength of the diaphragm, and the fill factor is raised drastically, consequently heat absorption energy increases and the output signal becomes larger.
Particularly, it is possible to carry out the etching of the silicon sacrifice layer and the anisotropic etching of the semiconductor substrate at the same time with the same etchant, such as hydrazine for example, by forming the projection made of the thermal conductor in the discontinuous wall or pillar-shape with a silicon material, such as polysilicon, whereby the concave is formed below the diaphragm.
In the production method of the thermal type-infrared detection device according to this invention, the concave is formed by combining the etching for the sacrifice layer and the anisotropic etching for the silicon substrate, therefore the sticking phenomenon between diaphragm and semiconductor substrate is avoided, thereby minimizing the height of the projection thermally connecting the cold junction area and the semiconductor substrate. That is, it is possible to make thermal resistance of the thermal conductor of the projection small and make a temperature difference between cold junction and semiconductor substrate negligibly small.
In the array of thermal type-infrared detection device according to this invention, the switching mechanism for device selection is disposed in the lower part of the infrared detection section and the cold junction area positioned on the diaphragm and the semiconductor substrate are thermally connected through the projection made of the thermal conductor, whereby the diaphragm is form in the same height from the semiconductor substrate and the fill factor is drastically improved without damaging the mechanical strength of the diaphragm.
Moreover, in the array according to preferred embodiment of this invention, the projections adjacent to each other of the respective devices are formed in continuous one body, thereby reducing a useless area between devices and an occupied area of one pixel, and consequently decreasing the cost of the device array.